1. Field
The present invention relates to a method for detecting an inter-axis offset of a 6-axis robot, which detects and compensates for an offset between a first rotation joint and a second, third, or fifth rotation joint, which have rotation axes perpendicular to each other.
2. Description of Related Art
A 6-axis robot is configured to convert given position data, which is expressed by fixed three-dimensional orthogonal coordinates, to angle data for a rotation joint of the robot and move an end effector (i.e., hand) of the robot to a position indicated by the position data. In this event, if an error occurs in a link (arm) length, an angle (hereinafter, referred to as a “twist angle”) between rotation axes of a rotation joint and a next rotation joint, or a relation between an origin position of a link and an origin position (hereinafter, referred to as a “motor origin position”) of a motor due to a working error or assembling error of components of the robot, or if a deflection is caused in a driving system of each rotation joint by an extra torque applied to the drive system, a deviation may occur in the position or posture of the end effector, so as to degrade the absolute position accuracy.
In order to improve the absolute position accuracy, various methods for compensating a rotation angle of a rotation joint in consideration of the error and deflection described above have been studied up to now. For example, “3-pair Joint Axis Estimating Method”, 4.3.2, page 52, a report on “Investigation research on standardization of intelligent robots for plants” (1997), JARA (Japan Robot Association) discloses a method of detecting and compensating for an error in relation to a link length and a twist angle. Further, patent documents of JPA 2003-220587, No. 2009-274186, No. 2009-274187, and No. 2009-274188 disclose methods for detecting and compensating for an error of a motor origin position. In regard to the deflection of a driving system, there is a known method, which compensates for the deflection of a driving system by calculating a load torque applied to a motor of each rotation joint from the mass and posture of each link, obtaining a twist deformation angle of a driving system from the load torque and a spring constant of the driving system, obtaining a deflection angle of each link from the twist deformation angle, and obtaining a motor rotation angle to reduce the deflection angle of each link.